题目已知两个电阻R1、R2并联后的总电阻为R,则有1R=1R1+1R2.现要求参加综合智能考试的同学用几何作图法求出总电阻的大小.经过一番思考,班里的小数学家张明、苗强、李伟分别想出了他们的做法.张明的做法是:如图1,作线段AB,过A作AC⊥AB,以一定的比例截取AC的长表示R1,再过B作BD It is known that the total resistance of two resistors R1 and R2 connected in parallel is R, then there is 1R=1R1+1R2. Now students who are required to take the comprehensive intelligence test are asked to calculate the total resistance using geometric mapping. After some thought, The small mathematicians in the class, Zhang Ming, Miao Qiang, and Li Wei, respectively figured out their practices. Zhang Ming’s approach is: as shown in Figure 1, for line AB, for A, AC⊥AB, to intercept AC in a certain proportion Long indicates R1, and B is BD